This proposed continuation of an established program provides training at the postdoctoral level in immunobiological, immunochemical and immunogenetic concepts and techniques with special emphasis on the study of problems related to the immune and the allergic response in pediatrics. The faculty of the Division of Immunology and of the Howard Hughes Medical Institute at Children's Hospital/Department of Pediatrics at Harvard Medical School has particular competence in the study of cell interactions, immunoglobulin gene rearrangement, immune deficiency diseases, mechanisms of T cell activation, animal models of immune deficiency, mechanisms of human IgE regulation and gene therapy. The participating faculty of the Departments of Pathology at Harvard Medical School, the Center for Blood Research, the Harvard School of Public Health, the Beth Israel Hospital, the Brigham and Women's Hospital, and the Joslin Diabetes Center provide additional expertise in immunogenetics, thymic development, adhesion molecules, autoimmune mechanisms, transcriptional control of cytokine expression, Fc receptors, co-stimulatory molecules, the T cell receptor complex and animal models of diabetes and inflammatory bowel disease. The groups have a record of collaborative work utilizing diverse approaches based on laboratory experience in cell biology, protein chemistry and molecular genetics in educating trainees in the fundamentals of research and in the application of their knowledge to clinical investigation in allergic, rheumatologic and immunodeficiency diseases. The training program consists of a three-year research experience. Support is requested for nine postdoctoral trainees having either an M.D. or Ph.D. degree or both and having had 0-3 years of biomedical experience before entering the program. For M.D.s, the program offers integrated training with a year of intensive training in clinical allergy/immunology/rheumatology, supported through clinical funds, followed by three years of research. The program continues to fulfill a need to train physician scientists in pediatric allergy/immunology/rheumatology, including members of underrepresented minority groups. Virtually all recent graduates supported by the Training Grant now occupy academic positions.